We seek to develop recombinant Lmdd, a vector generated from Listeria monocytogenes (Lm) by deleting two genes essential for the biosynthesis of the unnatural D-alanine (D-ala), as an oral AIDS vaccine. Without exogenous D-ala, the resulting vector, termed Lmdd, is unable to form cell walls or replicate. The first vaccine candidate, Lmdd-gag, was generated by stably inserting HIV gag into the Lmdd chromosome. In mice, Lmdd-gag, co-administered with D-ala, elicited long-lived CD8+ T-cell responses. In rhesus monkeys, wild-type Lm closely mimics infection and pathogenesis in humans (stillbirths, sepsis), who get infected mostly via contaminated food. Because of this natural oral route of Lm infection, Lmdd vectors hold promise as oral AIDS vaccines. In a pilot study, we administered Lmdd-gag orally to two monkeys with short D-ala courses; one monkey was boosted orally and developed cytotoxic T-lymphocyte (CTL) responses against HIV Gag, indicating that this candidate vaccine is immunogenic after oral administration. The other monkey developed strong antibody responses after i.m. boosting. The Specific Aims are to: 1. Test the hypothesis that oral vaccination will generate T helper type 1 (Th1) responses, whereas oral priming/i.m. boosting will result in Th2 responses. 2. Test safety, immunogenicity, and efficacy of Lmdd encoding SHIV89.6P gag, tat, or env. Groups of monkeys will be vaccinated with Lmdd encoding individual viral genes or with a combination all three vectors and challenged mucosally with pathogenic SHIV89.6P. 3. Test safety, immunogenicity, and efficacy of Lmdd encoding genes of SHIV-1157ip, which contains env of a HIV clade C isolated from a maternally infected African infant. SHIV-1157ip has been adapted to rhesus monkeys and replicates to high levels. Vaccinees will be challenged mucosally or intravenously with SHIV-1157ip. 4. Test long-term safety, immunogenicity, and efficacy of Lmdd vaccines against SHIV-1157ip in pregnant macaques and monitor long-term safety in Lmdd vaccine-exposed offspring. 5. Test safety, immunogenicity and efficacy of the best anti-SHIV1157ip Lmdd vaccine in newborn monkeys. These primate studies represent crucial steps towards developing recombinant Lmdd vectors for clinical trials as oral AIDS vaccine candidates that could be administered easily, even in the developing world.